Schematic diagram of the experimental setup. The transition from one contact angle hysteresis to another is shown as a dashed line.
The normalized acceleration of a 3.5 mm diameter droplet moving down an inclined plane of variable contact angle hysteresis and constant advancing contact angle of θ A = 150° as compared to the theory developed in Eq. (2) (dashed line).
Experimental setup with important parameters overlaid. The dashed line represents the location of the transition in contact angle hysteresis transition.
Sample droplet trajectories for transitions (on the left) from higher to lower contact angle hysteresis and (on the right) from lower to higher contact angle hysteresis.
Deflection of drops moving over a single transition in contact angle hysteresis presented as a function of the angle of transition, α T , for a range of Weber numbers between 0.05 and 1.25. The data include transitions from (■) 3° to 50°, (○) 3° to 15°, (●)15° to 3°, (∇) 3° to 30°, and (▼) 30° to 3°.
Normalized droplet deflection as a function of Weber number for single contact angle hysteresis transitions from (▼) 30° to 3°, (●) 15° to 3°, and from (∇) 3° to 30° all at a transition angle of α T = 40°. The inset contains the same data plotted against the modified Weber number proposed in Eq. (5).
Deflection of drops moving over a stripe of varying contact angle hysteresis presented as a function of the Weber number at a transition angle of α T = 40°. The data include (▼) a 3.5 mm stripe of 3° hysteresis among a surface with 30° hysteresis and (∇) a 3.5 mm stripe of 30° hysteresis among a surface of 3° hysteresis.
A low contact angle hysteresis surface with high hysteresis stripes of 3.5 mm in width. The resulting deflection is many times that of a single transition. The Weber number at the first stripe is We = 0.15, which is near the range of maximum deflection. Subsequent stripes result in further droplet deflection, however, each contribution is diminished because the droplet encounters them at higher Weber numbers.
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